Dielectric films with embedded silicon Si nanocrystallites (Si-Nc) have been recognized as promising light-emitting materials for future integrated photonics based on silicon technology. This work reports a novel method of making this kind of material by high-temperature annealing of Si-rich oxide or nitride films which gives rise to the phase separation reaction and the formation of crystalline silicon nanoclusters in the films. Various characteristics of these materials were studied in detail by using transmission electron microscope, X-ray photoelectron spectroscopy (XPS), Raman, and photoluminescence (PL). Strong transverse optical (TO) mode of Si-Nc at around 516 cm -1 was found in the Raman spectra of the annealed dielectric films. XPS studies indicate that the Si 2p spectra could be transformed from a random bonding structure (as-deposited) to a random mixing of Si-Nc with stoichiometric oxide or nitride phase after the high-temperature annealing. The energy locations of PL were found to depend on the amount of rich Si and the annealing conditions. Longer and higher temperature annealing can result in the growth of the Si-Nc size and leads to a red-shift of PL. Direct correlation among the crystallite sizes with the PL peaks was found .